Means for impregnating electric coils



@W 25, w H. c. STEARNS 294429183 MEANS'FOR IMPREGNATING ELECTRIC COILS iFiled sept. 25, w44

INVENTOR. Hy C Sitems WMS Patented May 25, 1948 COIL Harry C. Stearns,Glen Ellyn, Ill.l f Application september 25,1944, serial Nn. 555,725

2' Claims.

This invention relates generally to improvements in means for applyingand solidiiying varnish, and more particularly to improved means forvarnish impregnating electric coils,

When insulated copper wire has been wound into coils, to aiord aplurality of separated turns of conducting metal for thepassage ofelectric current, as for motor field coils, armature windings,transformer windings, magnet or solenoid coils and the like, these aregenerally dipped in insulating varnish, and then baked in ovens to forma non-hygroscopic covering of the whole coil. This anch'ors all of thewires into a solid unit to prevent rubbing of turns against theiradjacent turns, which would otherwise cause mechanical wearing away ofthe insulation f the wire itself. This is particularly true when dust ofany kind works into an unimpregnated winding. Vi-

brations set up by external forces, and vibrations l also be provided toprevent the entrance of moisture into th'e coils to lower insulationresistance and promote corrosion. These purposes are both accomplishedby the varnish impregnation and I baking.

In the process nowin use for treating the aforesaid coils with varnish,the coils are generally first subjected to high vacuum to removemoisture, or are subjected to elevated temperatures, or both,dependinglon the degree of moisture elimination required prior toimpregnation. High voltage applications generally require greaterelimination of moisture than do th'e lower voltage requirements, andquality jobs, or those where reliability and uniformity are essential,require moisture elimination comparable to the high volt ageapplications. The process is often very slow and expensive, as equipmentto handle coils in quantity is expensive, and length of baking timerequired makes .productivity of the equipment low.

After the vacuum treatment, or baking for this moisture elimination, thecoils go immediately into the varnish, where th'ey soak until al1openings are filled. This is sometimes done, also under partial vacuum,to eliminate trapped air, which also makes the operation slow andexpensive. The coils must remain in this treatment until all air iseliminated and all openings are filled. `This is particularly diilcultwhere fine wire is wound closely.

After the impregnation, coils are drained until y surplus varnish hasrun oil the outside.

Unless the vicosity of the varnish has been well controlled, it maydrain from the inside also, which is generally undesirable. Coils arethen usually placed in trays, which then go into ovens, for the bakingoperation, at temperatures which may be changed during the process.Beside the slow dimcult methods of the moisture elimination, thefollowing diillculties arise, in the baking operations, which areneedlessly slow, troublesome and often serious.

It is characteristic of solutions of gums, or plastics, in solvents,that the rate of solubility of the gums, or plastics, in these solvents,decreases as the solvent proportion lessens, and conversely, that therate ot ability of solvents to pass through such solutions is dependentupon the amount of solvent present in the solution For this reason, anundesirable solvent trapping eilect occurs during the baking, when thisis accomplished by external heat. This has been recognized in theapplication of radiant lamps to tlie drying of lacquer flims, as onIautomobile bodies. In this case the temperature of the metal sheet iselevated above the temperature of the lacquer lm, by the use oi.'radiant lamps. 'I'his elevated temperature of the metal sheet causes thedrying to start at the inner surface next to the metal, the solventbeing driven to the outside before a solid iilm forms at the surface.

. In the oven-baking method, the temperature of the outer film ofvarnish is elevated first, and the solvent thus dries from th'e outersurface more rapidly than from the mass of varnish within. Because ofthis condition, only very slow drying is possible, if bubbles orruptures are to be avoided in the insulation, due to the formation rstof the solid lm, on the outside, while considerable solvent must stillbe removed from within.

Since these ovens are expensive, with their close temperature controlequipment, and ventilation provisions for safety, the low productionrates make the operation costly. This needlessly ties up usuallyexpensive equipment and product in process, beside the other difcultiesaforesaid, and the slowness of the process causes other dimculties to beexplained later.

With reference to the radiant lamp method previously explained, it isevident that this method cannot be employed, as only the outer layer ofwire would be heated, `which would dry the outer film of varnishl beforethe mass of varnish within the coil has been dried.

The enamels used to insulate, or cover the wires, are soluble in many ofthe solvents used in the.

varnishes. Some of the enamels used, are soluble in naptha, benzene,kerosene and similar hydrocarbon solvents. Some are soluble in acetone,ethyl-acetate, amyl-acetate, and similar solvents, and some aredangerously soluble in mixtures of these and other solvents.

It is evident that when coils of wire insulated with these enamels aredipped into varnishes containing some or several of these or similarsolvents, that it is desirable to drive the solvent away from the enamelas rapidly as possible. I accomplish this, as an important improvement,in my process, as I will show, whereas in the present baking processes,the formation of the solid film on the outside of the coil preventsrapid elimination of the solvents. This also traps the solvents, atelevated temperatures, about the wires, to soften the enamel and -thusat times, permit the' turns to make metallic contact with eachother.This causes shortsf or the vsoftening may weaken insulation to laterpermit voltage breakdowns across these weakened spots, or to cause hotspots to ruin adjacent insulation.

I have found that if the temperature of each wire is elevated above thetemperature of the impregnating varnish, by internal heating of thewire, that the drying will start at this point. This immediately drivesthe solvent away from the enamel cover of the wire, thus protecting thewire cover, and setting up an internal drying rst, which is highlydesirable. This is one of the objects of my invention, i. e., to insurea better -average quality of product, by lessening hazards to enamelwire coverings. v

Another object is to eliminate handling from vacuum moisture removalovens, to dipping tanks, to baking ovens, and to accomplish this all inone automatic machine.

Another object is to reduce the amount of heat lost from themultiplicity of large ovens, and to confine the heat employed to auseful purpose in the machine.

Other objects of the invention will be evident as I proceed with thedisclosures.

Fig. 1 is a side elevation partly in section for4 automaticallyaccomplishing my novel methods of drying, impregnating and setting ofthe varnish.

Fig. 2 is a cross-section of the wire surrounded by a coating ofimpregnating varnish.

Fig. `3 shows one type of contact clip which may be used to makeelectrical contact with commutator bars, when armatures are impregnated,and also support the whole assembly mechanically.

Fig. 4 shows a modification wherein a laminated stator stack issuspended in a high frequency magnetic field.

In Fig. 1, the frame of the machine is designated 2, which rests uponthe bed 3. A tank 5, containing impregnating varnish 1, is shownsupported by the bed 3. The upright portions of frame 2 are providedwith vertical slots 4, within which the cross-shaft 6 is moved byconnecting rods I5. Shaft 8, revolving in bearings 9, is driven at timesduring the process by motor I0, through gear reduction unit II, off-setcounter shaft 8a and pinion I3b. The shaft 8a is journaled in bearingI2, and pinion I3b is in meshing engagement with the external teeth ofplate I3. As shown in Fig. 1, the plates I3 and I3a are xed for rotationwith shaft 8, and accordingly 4 any special coils, or armatures such asI1 shown in Figs. 1 and 3. These attachmentsv not only, support thearmature or coil but' make electrical contact, as on the commutator barsI8 or the vclipping of the bare wire ends of the coils. The

fixtures I6 are similarly constructed, in principle, to electric lightsockets to permit separated'electrical leads to be connected to them topass electric current through to the fixtures I8, with their separatedcontacts, to the coli terminals in the' commutators I9.

The control unit is shown as 20, Fig. 1. A synchronous or constant speedmotor 2|, with built-in speed-reducer, turns the drum 23 at the desiredspeed for a maximum cycle of time for one full operation. The metal drum23 is excited, by one side of the line, over the same switch!! whichstarts the synchronous motor 2|. The metal drum is covered with aninsulating sheet with slots 24, 25 and 26. which permit the brushes 21,28 and 29 to make contact with the metallic drum in the proper sequence.28 and 29, when excited by contact with the metallic drum 23, actuaterelays 30, 3l and 82v over the circuits shown. A greater number of thesebrushes and circuits may be used where more current changes are needed.Resistance coils 34 and 35 are used in the circuits to control currentdemands, but transformers or autoformshaft 8 is elevated and lowered inthe slots 4 by ers could be used with alternating current, which mightbe used with the armatures shown, to heat their iron stacks byinduction. The line 31 leads to ground, and 38 leads from the controlunit.to the holding fixtures I6 to supply current for the processing ofthe windings and stack.- Lines 39 and 40 lead from the contro1 unit tothe motor I0.

Fig. 2 shows a copper wire 4I surrounded by a film of varnish 42. Thearrows show the direction of heat loss and temperature drop, and theregion of heavy dots in the varnish film shows where the fast dryingstarts.

is shown as 48 supporting the insulated copper wire coil 50. Leads tothe copper 4wire coil .are shown as 5I and 52.

In operation, when the armatures or coils have l been suspended inclips, as shown in Fig. 1, the switch 22 is thrown. This excites thedrum 23, as previously stated, and starts the motor-- 2|. When the drum23 has turned a short distance it picks up contact with brush 21 throughslot 2L IIhis pulls in relay 30, which causes the current regulated byresistor 34 to pass through the armature windings, to dry the moisturefrom same. The length of time, before slot 25 makes contact with brush28, controls the time' of drying.' At this point, and while the armature.is still warm, the exciting of brush 28, by making drum contact throughslot 25, pulls in relay 3|, which causes the motor I0 to lower thearmatures I1 into Athe varnish 1.. It will be noted that the currentcontinues to flow through the coils after they have been immersed. Thisis for the purpose of thinning the varnish, as it flows into thewindings, to insure good penetration because of its lowered viscosity.When this has been'accomplished, the current is cut off at the limit ofslot 24. The current remains off, to allow thickening of the var- Thesebrushes 21 nish in the windings, until the second slot 25 is reached,when the motor I0 is again excited, thus lifting the shaft 6 and coilsl1 out of the varnish. At this point, contact is made at 26 with brush29 to actuate relay 32, to pass the proper amount of current throughimpedance or resistance 35 to drive out the solvents from the windingsand hold the temperatures of the windings at that desired to set thevarnish. With gloves, the armatures or coils may then be removed fromthe 'clips I8 and laid in trays to cool. Removal of the solid varnishfrom the commutators and armature poles would be accomplished in themanner previously used.

I have now described the oper-ation of the machine suited to my processor method. I have accomplished my objectives by passing the properamount of electric current through the coils to ilrst dry out allmoisture, from the inside toward the outside. I have heated the heaviervarnish close to the turns during impregnation, to lower its viscosity,and thus permit it to rapidly enter all openings after it has driven outany air by outward expansion, due to internal heating. I then cut oil?the current to let the varnish cool within the windings, to become heavyand viscous, before removing coils from varnish, to lessen internaldrainage. I then accomplish the ilnal drying and baking by passage ofelectric current of the proper intensity, or change of intensity throughthe windings. Change of current intensity may be accomplished by usingseveral brushes, with different resistances, instead of the one brush2l, Fig. 1. By picking up and dropping these in the proper sequence,maximum rapidity of drying, outwardly from around' each wire, isaccomplished, because maximum tolerable internal heat conditionsprevail, with the surface of the varnish still soft, with no crust orsolid film to retard drying, as previously stated.

Alternating current, oi the proper frequency, may be employed in thecoils, when they surround a laminated stack of iron, to set up heat ineach lamination to dry and set the separating varnish, in this manner,by liberating the heat from within. Frequencies and current intensitiesare adjusted to accomplish the required balance for the double purpose,with an automatic process,

for heavy production, generally similar to thatv shown in Fig. 1, topermit the sequence of operations to be controlled automatically, aswell as to control the frequencies and current intensitiesautomatically. 1

It is sometimes desirable to impregnate a laminated core before winding,such as an amature stack assembly 41 (Fig, 4) or a stator stack aslsembly, to fill all of the openings between the laminations, to lesseneddy currents and to eliminate humming in the nished product. It may bedesirable to use a heavier varnish, for this purpose, or a differentvarnish from that desired in the windings.

'I'hese may be treated in the following manner: The cores are hung in afixturey suspended on the machine in a manner similar to that shown inFig. 4. The stack is hung on a hook within a coil of wire. The properhigh frequency current is passed through-the coil to elevate thetemperature above the temperature of the varnish, to first accomplishdrying at the inner surface, as I do n in my coil drying. The sequenceof operations, in this case, is similar to those previously described.

Individual laminations couldbe passed through special machines toaccomplish the same sequence to rapidly coat them with dried varnishalso.

While I have shown one means for accomplishing my objects, it could b ealtered to accomplish good results. It is possible that varnishes mightbe used, in which the main solldifying of the impregnating uid might beaccomplished by polymerization due to heat. My machine would have manyadvantages in this case also. For this reason I do not propose to belimited to the exact disclosure, but to the broad principles of theinvention.

Having disclosed my invention, what I claim is:

1. An apparatus for impregnating coils of electrically insulated wirecomprising in combination a tank containing an impregnating varnish, across member vadapted to support a plurality of coils to be impregnated,means to raise and lower said cross member to dip all of said coils insaid varnish, means to pass current through said coils to eliminatemoisture therefrom, and automatic means to sever the current flowthrough said coils during a period when they are submerged in saidvarnish to prevent internal drainage upon their removal from thevarnish.

2. An apparatus for impregnating coilsof electrically insulated wirecomprising the combination of a tank containing an impregnating varnish,a cross member adapted to electrically support a plurality of coils tobe impregnated, means to raise and lower said cross member tosimultaneously dip all of said coils in said varnish, electrical meansarranged to pass current through said coils before they are dipped inthe varnish to drive moisture therefrom, and automatic means to severthe current ilow through said coils during a period when they aresubmerged in the varnish to allow thickening of the varnish to preventinternal drainage upon their removal from the varnish, said lastmentioned means adapted to re-establish said current flow through thecoils upon their removal from thevarnish to dnive solvent out andsolidify the varnish from the coils outwardly to prevent rupturing ofsaid varnish during its drying period.

HARRY C. STEARNS.

REFERENCES CITED The following references are of record in the GreatBritain 1905

